The present invention relates to an electrowinning process for the recovery of one of a plurality of metals from an aqueous electrolyte and more specifically to such a process carried out within an electrolytic cell containing spaced apart anodes and cathodes with the anodes being formed from lead or a lead alloy.
Electrowinning processes are widely employed for recovering one of a number of metals from an aqueous electrolyte solution containing ions of the particular metal. Metals suitable for refining by electrowinning processes include, but are not limited to copper, zinc, nickel, antimony, cadmium, chromium, cobalt, manganese and silver. The electrolyte solution is typically placed within an electrolytic cell containing spaced apart anodes and cathodes which are commonly arranged in alternating order. The electrolyte may be a solution of sulfates, sulfides, caustic or nitrates depending upon the particular metal to be refined by electrowinning. During operation, an electrical potential is formed between the anodes and cathodes in order to cause the metal ions from the aqueous electrolyte to deposit upon the cathodes by conventional electrolysis.
In electrowinning processes of the type summarized above, the aqueous electrolyte solution, containing sulfuric acid, in the electrowinning of copper, for example, tends to corrode the surface of the anodes. When the electrowinning process is continued over long periods of time, corrosion not only results in the introduction of lead from the anodes as an impurity in the metal deposited upon the cathode but also results in destruction of the anodes themselves. This in turn disrupts the electrowinning process and requires costly replacement of the relatively massive anodes.
In the prior art, various alloys have been employed for forming such anodes in an attempt to resist corrosion of the type referred to above. One of the earlier replacements for pure metallic lead in the anodes was an alloy formed from lead in combination with antimony. Later, the use of lead-calcium alloys as inert anodes in electrowinning processes for the recovery of copper was disclosed for example by U.S. Pat. No. 3,859,185 issued Jan. 7, 1975.
However, even with the use of such alloys, corrosion has continued to be a problem in electrowinning processes for the recovery of metals such as copper. Accordingly, in view of increasing requirements for various metals subject to refining by means of electrowinning, there has been found to remain a need for an improved electrowinning process employing an insoluble anode and more particularly for such an improved electrowinning process carried out in an electrowinning cell containing spaced apart anodes and cathodes.